The incident happened during the 77th over when Smith was batting on 80 from 152 balls and delivery by Archer hit him on the unprotected part of the neck. The medics ran into the middle from both sides, as the England players rushed to the former Aussie skipper immediately.
As Smith lay on his back before slowly getting back on his feet, he looked dazed. The medics forced him to leave the field with Australia at 203/6, still, some way behind England's first innings score of 258.
Later, he returned to the middle after Peter Siddle’s dismissal in the 86th over. However, he could spend just 15 more minutes as he as trapped by Chris Woakes in the front on 92. He may have had missed his 3rd consecutive century in this tour but received huge round applause on his way back to the dressing room.
Earlier at lunch, Smith had chiselled England's lead down to 103, guiding Australia to 155/5. Smith was batting on 53 off 122 balls (4x6), his seventh consecutive Ashes half-century, with skipper Tim Paine giving him company on 21 (63 balls).
In the first Test, which Australia won by 251 runs, Smith notched up centuries in each innings to put up a masterclass display of five-day batting in a completely unorthodox fashion.